5:2 molecular motors: from bacterial motility to anti-phage defense

Bacteria move through the rotation of large filaments know as flagella. Flagellar rotary motion is powered by a flagellar motor, driven by stator units (MotAB). The MotAB proteins convert the ion motive force across the bacterial inner membrane into rotation of the filament, but it was not understood how this occurred.

Using cryo-EM we have determined structures of the MotAB complex, which we show has a 5:2 stoichiometry shared across different species. By visualizing MotAB in its plugged, inactive state, as well as mimics of its active state, we come up with models for how torque is generated in the flagellar motors, as well as how direction switching in the flagellar motor occurs. We also reveal our recent progress on how ion specificity is obtained and propose a mechanism for how stator units become active upon motor incorporation.

I will also present results on a newly discovered bacteriophage defense system, Zorya, that uses a 5:2 motor complex to sense bacteriophage infection. Using a combination of structural biology, functional assays, light microscopy and mass spectrometry, we provide novel insight into the unique Zorya mechanism of action. We provide data indicating that Zorya detects phage infection by monitoring integrity of the peptidoglycan layer. Upon phage infection, the ZorAB motor proteins get activated and through a 700 Å long tail locally recruit and activate ZorD nuclease that can degrade the phage genome, halting the infection.